The TriStar fuel pipe issue came about due to someone's clever idea
to have an operational reason to refuel from both pods and the centreline hose simultaneously. Under such circumstances, the original pipe size would have been inadequate... Then those with a little more operational knowledge than some of the MoD advised that 3-point simultaneous prodding would be highly risky anyway and would also require the pod hoses to be extended so that all 3 receivers could keep an eye on each other. By then the whole TriStar pod issue was getting increasingly late and doubtful, plus the VC10K4 and VC10C1K would soon be entering service...
A pity that the TriStar never had pods - it would have been extremely useful with multi-hose capability and a massive fuel offload potential.
All history now though.
As for the F-35, I thought that it was originally seen as an F-16 / F-18 replacement, low cost (hah!) and stealthy? Which meant that it would cover all the roles of the F-16 / F-18 (and Harrier), so was never conceived as a single role fighter. That's the job of the superb F-22 - a great pity that the USAF order was curtailed.
Anyway, back to tankers. How's the KC-46A going down with the end users now that they've finally got their hands on it?